This invention relates generally to systems and devices for controlling hydraulic motors and in particular relates to such systems and devices for aircraft hydraulic systems that are referred to as "fly-by-wire". In such systems electrical signals originating at a remote command station are transmitted to electro-hydraulic servo valves that control master valves that direct flow of fluid to and from hydraulic motors. For safety reasons the systems employ redundant components and control channels so that the system will operate despite failure of some of the components and/or control channels. Such redundancy is particularly important in fly-by-wire systems because the electrical components do not have the high degree of reliability that mechanical and hydraulic components provide.
In previous fly-by-wire systems various methods have been employed for detecting, correcting and/or overriding failed components and control channels so that the hydraulic motors could be operated in a proper manner despite such failures. These methods have not been entirely satisfactory because of complexity, time lag in compensating for failures, and other reasons.